Si prova la maggior sommabilità del gradiente dei minimi locali di funzionali integrali della forma $${\int }_{\mathrm{\Omega }}f\left(Du\right)dx,$$ dove $f$ soddisfa l'ipotesi di crescita $${\left|\xi \right|}^p-c_1\le f\left(\xi \right)\le c\left(1+{\left|\xi \right|}^q\right),$$ con $1<p<q\le 2$. L'integrando $f$ è $C^2$ e $DDf$ ha crescita $p-2$ dal basso e $q-2$ dall'alto.

In this paper we consider a class of integral functionals whose integrand satisfies growth conditions of the type $$\begin{array}{c}f(x,\eta ,\xi )\ge a\left(x\right)\frac{{\left|\xi \right|}^p}{{(1+|\eta \left|\right)}^{\alpha }}-b_1\left(x\right){\left|\eta \right|}^{{\beta }_1}-g_1\left(x\right),\\ f(x,\eta ,0)\le b_2\left(x\right){\left|\eta \right|}^{{\beta }_2}+g_2\left(x\right),\end{array}$$ where$0\le \alpha <p$, $1\le {\beta }_1<p$, $0\le {\beta }_2<p$, $\alpha +{\beta }_i\le p$, $a\left(x\right)$, $b_i\left(x\right)$, $g_i\left(x\right)$ ($i=1$, $2$) are nonnegative functions satisfying suitable summability assumptions. We prove the existence and boundedness of minimizers of such a functional in the class of functions belonging to the weighted Sobolev space $W^{1,p}\left(a\right)$ , which assume a boundary datum $u_0\in W^{1,p}\left(a\right)\cap L^{\mathrm{\infty }}\left(\mathrm{\Omega }\right)$.

Let $L$ be a second order, uniformly elliptic, non variational operator with coefficients which are bounded and measurable in ${\mathbb{R}}^d$ ($d\ge 3$) and continuous in ${\mathbb{R}}^d\setminus \left\{0\right\}$. Then, if $\mathrm{\Omega }\subset {\mathbb{R}}^d$ is a bounded domain, we prove that $L\left(W^{2,p}\left(\mathrm{\Omega }\right)\right)$ is dense in $L^p\left(\mathrm{\Omega }\right)$ for any $p\in \left(1,d/2\right]$.

We study degenerate elliptic problems of the type $$\left\{\begin{array}{cc}-\text{div}\left(\frac{\nabla u}{{(1+|u\left|\right)}^{\theta }}\right)=f\hfill & \text{in}\Omega \hfill \\ u=0\hfill & \text{on}\Omega .\hfill \end{array}\right.$$